Loud-speaker



1929 P. F. FlNDElSEN ,74 6

LOUD SPEAKER Filed April 10. 1925 Z-ShEetS-Sheet l m I J INVENTOR PAUL F. FINUEISEN ATT RNEY Dec. 24, 1929. R FlNDElSEN I 1,740,446

LOUD SPEAKER Filed April 10. L925 2 Sheets-Sheet 2 NNHHHA 5 BA LIL I .-'V f j v INVENTOR PAUL F. FINDEISEN TTORNE'Y as pure a timbre as possible may be produced Patented Dec. 1929 UNITED STATES PATENT OFFICE PAIFL FELIN FINDEISEN, F BERLIN, GERMANY, ASSIGNOR T0 GESELLSCHAFT F'lj'R DRAE'I'LOSE TELEGRAPHIE M. B. 1-1., 01'! IBEBL IN', GERMANY, A CORPORATION OF GERMANY LOUD-SIPEAKER App1ication fiiea'a i-n 1c, 1925, Serial no. aaoisyana'm Germany April 25, 1924.

My invention relates to electro-acoustic devices by means of which energy in the form of sound waves emanating from any source of sound is changed into electrical energy, or, conversely, electrical energy in the form of the corresponding sound variations is changed into energy in the form of sound waves.

An object of the invention is to provide a device of this character that will be free from distortion to the greatest possible extent.

Other objects will be apparent from the following description and'claims when consideredwith the accompanying drawing in which:

Fig. 1 is a diagrammatic illustration of one embodiment of my invention.

Fig. 2 is a diagrammatic illustration of another modification.

Fig. 3 is a diagrammatic illustration of a combination of the first two modifications.

Fig. i is a cross section on the line 4rl of either Fig. 2 or Fig. 3, showing also the individual sound horns leading to a single common horn.

It is a well-known fact that in loud-speakers in which acoustic vibrations are produced by virtue of the vibration of a membrane or diaphragm, marked distortion of the sound vi-. brations are caused due to the natural frequency of the diaphragm. In order that sound transmission free from distortion may be obtained, it is necessary to use, either diaphragm whose natural frequency does not fall inside the range of sounds or tones, or else elements must be chosen for the transmission of sound possessing a great number of natural frequencies so that corresponding resonance frequencies are obtained for the sounds to be transmitted. 7

Now, the present invention has recourse to the latter arrangement. It has been discovcred that a satisfactory rendition of sound is made possible if, instead of a diaphragm, steel chords are used which are set into vibration for difierent tones, it is necessary that a great number of chords be exposed to the influence of the current variations caused by the sounds.

This can be done in various ways as explained in the fol lowing description.

For instance, it is possible to influence several chords by the fields of a single telephone magnet, in a way as diagrammatically illustrated in Fig. 1, in which m, m, are the v pole shoes of an electro-magnet over which seven chords 0 of varying length are stretched, as'indicated in the drawing. The chords are fastened on a ring 1'. For tuning,

if desired, screws D can be used by means of which readjustment in tension is possible.

Taken together, the tensioned chords act just like a diaphragm possessing a plurality of -natural frequencies.

Another plan of carrying the. idea intopractice would be to furnish each telephone magnet with just one chord, and to use at the same time a plurality, or a great number, of such magnets in the case of which each chord possesses its own natural period. This arrangement is shown in Figs. 2 and 4;. A base plate P has a number of openings therein into justed by, adjusting devices D of any eonvenient kind arranged near. the periphery of -plate P.

Each element 1 to 7 inclusive has a-cap R the'reover, (see Fig. 4) said caps each supporting a small horn H. Theouter ends of horns H open into 'plateK which forms part of alarge common horn'L. This is a very favorable arrangement, the sound vibration horns being supplied from each of the small to the single large horn.

The individual magnets M are connected in parallel. 1

The number as individual sound transmit} ters to'be used,'as a generalrule, may prob- At the center of the base plate P is an i ably have to be chosen difl'erent' according to the sounds to be transmitted. For transmis sion of music, faithful transmission or'reproduction is realizable by having the steel chords correspond to the seven fundamental lUU the end of the core and tuned to vibrate only at a predetermined frequency. a

' 3. A sound reproducer comprisinga plu,

soundsof the scale.- The letters (1,6, 0, d, ej,

f and g, indicated with the chords in Fig. 2

correspond to the seven fundamental tones.

. sired, so that It goes without saying that for the object of changin the pitch ofthe chords, bridge eusem' orelse'other well-known I means for the same object. In. the case of o transmission of music made, for instance, by; wind (brass) instruments, the distortion of the tones due to natural frequencies of a dia. I phragm becomes by farless noticeable. than I' for string instruments-' or, piano music, Hence, arrangements may'falso be so chosen c that a telephone magnetis' provided with a 1 good diaphragm which may'preferably be disposed so as'to be disconnected-when de i itcanbe used only when re- 7 pieces can 7 'quired.

Now referring to Figs. 3 and 4,wherein is showna combination of the first two embodiments, actuating eleme'nt6 isshown provided with seven chords which may have their natural periods arranged according to the seven fundamental tones in the manner of the modification shown by the described in connection with Fig. 1;

Furthermore, anyone of the other actuating elements may have "one or more chords which chords-may be arranged so that their natural periodshave any desired values.

Having described several embodiments of my invention, I am entitled to all modifications thereof as fall fairly Within the spirit and scope of the following claims:

1. An electro-acoustic device comprising electro-magnetic means having a core which in cross section has parallel sides, and seven chords of magnetic material stretchedtransversely of the-end of said core, each of said chords being tuned to a different one of the seven fundamental tones in an octave of the musical scale,

a 2. Means for the 'intertransposition tr sound and electrical energy comprising a sound chamber and a plurality of electroacoustic devices cooperating therewith, each of said devices comprising electro-magnetic means includmga core WlllCh 1n cross section ments, and a single horn for collecting and --amplifying the sound waves from said sepa-- has parallel sides, andone. or more chords of magnetic material stretched transverselv of ralityo'f vibrato'ry elements'each of which issuspended to vibrateiat a predetermined natural period different from the natural periods of the other vibratory elements, means. for vibrating saidelenients at their natural periods, a separate sound collecting and amplifying horn for each of said elerate horns.

mun FELIN FINDEISENQ 

